Ischemia reperfusion (IR) induced renal injury causes acute renal failure and is associated with high morbidity and mortality rates. The cellular mechanisms underlying IR renal injury are not known. Meprins, metalloproteases that are abundantly expressed in the brush border membranes (BBM) of proximal kidney tubules, have been implicated in the pathology of IR. Mice strains with lower levels of meprins develop less renal injury when subjected to IR. Meprin inhibitors and targeted disruption of the meprin gene both protect mice from IR induced renal injury. We recently demonstrated that meprins cleave actin and villin, the key components of the proximal tubule cell cytoskeleton, suggesting that the observed renal injury is in part due to degradation of cytoskeletal proteins. Meprin B also cleaves the catalytic subunit of protein kinase A (PKA), a protein that modulates many cellular signaling pathways. OS-9, a protein involved in the hypoxia response, has been shown to interact with the carboxyl-terminal tail of meprin. However, it is not known if OS-9 is a meprin substrate, and whether interaction between OS-9 and meprin plays a role in the pathology of IR induced renal injury. The broad long term goal of this project is to elucidate the cellular mechanisms responsible for IR induced kidney injury, and facilitate development of therapies to prevent IR associated renal failure. The central hypothesis is that meprins play a key role in the injuries observed in renal IR. This is in part due to cleavage of cytoskeletal proteins (such as villin and actin), proteins present in tight junction complexes, and extracellular matrix (ECM) proteins. Meprins may also play an indirect role by cleaving proteins that modulate specific signaling pathways (such as PKA and OS-9) and thus impacting expression of genes driven by these pathways. The proposed studies will use meprin knockout mice and proteomic approaches to identify meprin associated proteins that play a role in IR and elucidate underlying cellular mechanisms. The central hypothesis will be tested by pursuing the following three specific aims: (i) to identify meprin-associated proteins that play a role in IR induced renal injuy, (ii) to determine the role of meprins in cytoskeletal remodeling associated with IR induced renal injury, (iii) to determine if interactions between meprins and cell signaling molecules play a role in IR induced kidney injury. Results from the proposed studies are expected to have an important positive impact because elucidating the mechanisms underlying IR induced renal injury will facilitate development of therapies for preventing acute renal failure due to IR.